1. Field of the Invention
The present invention relates to an information storage medium on which data is recorded using an optimal writing strategy to achieve high-speed recording while improving jitter characteristics and a method and apparatus for recording data on the information storage medium.
2. Description of the Related Art
An optical pickup performs non-contact recording/reproducing to/from an information storage medium such as an optical disk. Optical disks are classified into compact disks (CDs) and digital versatile disks (DVDs) depending on data recording capacity. Examples of optical disks capable of writing and reading information include 650 MB CD-Recordable (CD-R), CD-Rewritable (CD-RW), 4.7 GB DVD+R/RW, DVD-Random Access Memory (RAM), and DVD-R/RW. Examples of read-only media include 650 MB CD-ROM and 4.7 GB DVD-ROM. Furthermore, high definition-DVDs (HD-DVDs) with recording capacity of over 20 GB are currently being developed.
When writing data on an optical disk, which is one type of an optical recording medium, marks are created in tracks on the optical disk. For read-only disks such as CD-ROM or DVD-ROM, marks are produced in the form of pits. For recordable disks such as CD-R/RW and DVD-R/RW/RAM, a recording layer is coated with phase change material that changes between amorphous and crystalline states. A laser is focused on the phase change layer to create amorphous marks. For the recordable disks, different writing strategies are implemented for a disk to optimize the recording and/or reproducing performance. Since recording conditions may also vary depending on the type of a drive, the drive may not be compatible with an optical recording medium.
From a signal detection perspective, a data recording method is classified into mark edge recording technique and mark position recording technique. In a mark position recording technique, the amplitude of a detected RF signal changes from positive-negative to negative-positive at a point where a mark is written. On the other hand, in a mark edge recording technique, the amplitude of a detected RF signal changes from positive-negative to negative-positive at both edges of a mark. Thus, writing the mark edge accurately is critical for increasing the quality of a RF signal.
However, for a disk having a phase change layer, the shape of a trailing edge of a mark written varies depending on the length of a mark or a space between marks. That is, the trailing edge of a mark written according to the conventional recording technique, which is longer than the leading edge, is one of the factors that degrade recording and/or reproducing performance. Longer recording marks results in such degradation due to heat buildup.
FIG. 1 shows a recording waveform produced when recording Non Return to Zero Inverted (NRZI) data according to a conventional recording technique. T is the duration of a reference recording/reproducing clock signal. In mark edge recording, high and low levels of NRZI data are recorded as mark and space, respectively. A waveform used for recording marks is called a write pattern while a waveform used for recording spaces (or erasing marks) is called an erase pattern. The conventional recording waveform uses multi-pulses as a write pattern, and the power level of each pulse is adjusted using Pw, Pe, and Pb that are write power, erase power, and bias power, respectively. That is, the power levels Pw and Pe are used for a multi-pulse in the write pattern. In particular, power Pe used for the erase pattern is kept at a predetermined DC level.
Since the power level Pe in the erase pattern of the conventional recording waveform is kept at a specified DC level for a predetermined period of time, heat in a temperature range of 0 to 200° C. is continuously applied to a region to be erased. Repeating a writing operation numerous times results in distortion of the shape of a mark, thereby significantly degrading the recording and/or reproducing characteristics. In particular, this degradation becomes more severe when the duration T of a reference recording and/or reproducing clock signal decreases and thermal interference between pulses in a recording waveform increases as demand for high density and high speed recording increases.
That is, since erase DC power is applied to erase recorded data during recording, carrier-to-noise ratio (C/N) in a recorded and/or reproduced signal decreases due to thermal interference between write pulses. This also causes incomplete formation of recording marks (partially crystallized) as well as degradation in reproducing characteristics. During high-speed recording intended to increase data transfer rate, the degree of distortion in a recorded and/or reproduced signal significantly increases. Furthermore, the use of a multi-pulse as a write pulse necessary for high-speed recording causes residual heat that adversely affects successive marks or spaces. The heat buildup due to such excessive use may result in abnormal formation of marks.